JPH07121966B2 - Controlled rheology polypropylene - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to the removal of tert-butyl alcohol (TBA) with a reduction in molecular weight and a restriction of the molecular weight distribution of polypropylene during extraction.

When an organic peroxide is mixed with polypropylene in the melt phase, it causes the polymer to decompose to a low molecular weight. The resulting polypropylene also has a narrower molecular weight distribution than the starting material and exhibits improved flowability during fabrication of the final plastic product. Commercially available polypropylene produced in the presence of organic peroxide has controlled rheology (C
R) Known as resin. Although many types of peroxides are available, certain peroxides [2,5-dimethyl-2,5-bis (t-butylperoxy) hexane] give CR polymers because of their unique decomposition temperatures. It is the peroxide of choice in the manufacturing industry. Lucidol Division of Pennwalt C
Lupersol sold by orp.)
101 is such a peroxide.

Although the CR resin made with Lupersol 101 shows good processability, it contains different amounts of TBA. When heated, these resins give off the unpleasant odor of TBA. Also, government regulations have recently limited the amount of TBA present in polypropylene resins or products to 25 ppm.

Background Art Prior to the present invention, the processability of polypropylene is
It was known to be improved by incorporating small amounts of peroxide compounds into polypropylene. This peroxide compound was typically added to polypropylene particles or pellets, sometimes in an inert gas, before being placed in an extruder, melted and controlled by heating and / or mechanical energy of a screw or mixer. , Extruded into pellets, films, or sheets with predictable flow characteristics.

Peroxide compounds have been described as free radical initiators in US Pat.
With reference to 4,436, in this patent they are used to improve the melt index of the product in the extruder.

Aliphatic peroxides have been used with crystalline polypropylene powder in US Pat. No. 3,887,534 to improve intrinsic viscosity and melt flow.

In U.S. Pat.No. 3,940,379, the controlled oxidative degradation of polyethylene is carried out by the use of other peroxides, which patent describes essentially the color of the product obtained with minimal oxidative degradation and minimal thermal degradation. And emphasizes its odorless properties.

Many patents teach the crosslinking of polyethylene by the use of peroxides-U.S. Pat.Nos. 3,846,396, 3,917,7.
See 45 and 3,963,673.

One of the peroxide compounds we use is 3,6,6,9,9-
Pentamethyl-3-n-propyl-1,2,4,5-tetraoxacyclononane is included in the general formula of the group of peroxides disclosed in US Pat. No. 4,271,279 as being effective in cross-linked polypropylene. Compounds of this general formula are effective in improving the processability of propylene copolymers, US Pat.
It is shown in No. 451,589.

The reader will be interested in U.S. Pat. No. 4,460,750 which shows the treatment of peroxides to produce transparent films of ethylene copolymers.

DISCLOSURE OF THE INVENTION The general formula tendency of many prior art peroxide additives to give TBA is eliminated by using our invention. That is, the particular peroxide used to improve the processing properties of polypropylene has a desired half-life and is selected for its ability to degrade polypropylene in a controlled manner without forming TBA.

The present invention provides TB during the production of CR polymers by peroxide decomposition.
Eliminate the formation of A. The method is carried out in the presence or absence of air. The product also exhibits good color and equal processability and physical properties as compared to the resin made with Lupersol 101. This is 2,2-di (t-amyl) peroxypropane (lupersol 553 of lucidol) or 3,6,6,9,9-pentamethyl-3-n.
-Propyl-1,2,4,5-tetraoxacyclononane (Esperal 529 of Peroxy John Division of Wicochem).

In the process of the present invention, a known amount of peroxide is premixed under nitrogen with a polypropylene powder containing conventional additives or stabilizers. The polypropylenes for which our invention is useful include copolymers with up to 10% ethylene.
The polypropylene / peroxide mixture was added to a mixer or extruder under a nitrogen purge and mixed with mixing 18
Preheated to 0 ° C.

Our peroxide material should be added to polypropylene pellets, flakes or powders at concentrations of 50-10,000 ppm. This component (polypropylene powder, peroxide, and additives) is premixed at room temperature and then in an extruder at a temperature not exceeding 550 ° F, or polypropylene powder and additives are premixed at room temperature and peroxide The ingredients are either added to the extruder at the same time, or all ingredients are premixed in a heated mixer not exceeding 550 ° F prior to addition to the extruder.
This mixing should occur at 350-550 ° F.

Our material is a peroxide compound with a half-life of 1.0-10 hours at 128 ° C, which does not decompose to TBA. This means that no peroxide material remains in the polypropylene under the extrusion conditions described above. In particular, our material is 2,
2-di (t-amyl) peroxypropane and 3,6,6,
It is selected from the group comprising 9,9-pentamethyl-3n-propyl-1,2,4,5-tetraoxacyclononane. When using a Banbury mixer at 20 rpm, if all samples were added, increase the mixing speed to 80 rpm and continue mixing at 180 ° C. under 10 kg ram weight for 1-3 minutes. At the end of this time, transfer the material under nitrogen, cool and grind to a powder. When this method was performed, comparative molecular weight and TBA content were measured on the samples. The results are shown in Table I.

Similar tests were conducted in a 1 inch yellow jacket extruder and the results obtained are shown in Table II.

The results show that at the same concentration, lupersol 553 was not as effective as lupersol 101, but when TBA was completely removed from this system, lupersol 5
May increase the concentration of 53.

Tables III and IV show the data collected on the other two extruders.

Claims (8)

[Claims] 1. A method of improving the processing properties of polypropylene, wherein the peroxide compound is mixed with polypropylene,
It has a half-life of about 1 to about 10 hours at 128 ° C, and t-
About 50 to 10,000 ppm of a peroxide compound that does not decompose polypropylene is added to butyl alcohol and the mixture is melted under thermomechanical action to form a solid polypropylene product free of peroxide compound and t-butyl alcohol. An improved process which comprises reducing the molecular weight of the polypropylene product, increasing the melt flow and narrowing the molecular weight distribution. 2. A method according to claim 1 wherein the thermomechanical action is performed at about 330-550 ° F. 3. The method of claim 1 wherein the thermomechanical action is performed at about 350-500 ° F. 4. The method of claim 1 wherein the peroxide compound is mixed at about 40-500 ppm. 5. The polypropylene product is pellets.
The method according to claim 1. 6. The method of claim 1 wherein the polypropylene comprises up to about 10% ethylene. 7. The method according to claim 1, wherein the peroxide is 2,2-di (t-amyl) peroxypropane. 8. A peroxide is 3,6,6,9,9-pentamethyl-3.
The method of claim 1 which is n-propyl-1,2,4,5-tetraoxacyclononane.